Researchers at the University of Maryland are urging for greater monitoring of avian flu in domestic cats. This call comes after a global review of two decades of data showed a significant rise in feline infections, particularly following the emergence of the H5N1 clade 2.3.4.4b in other species.
The scientists expressed concern in a recent Open Forum Infectious Diseases publication, stating, “Infections among mammalian species in frequent contact with humans should be closely monitored.” They pointed out that domestic cats are vulnerable to avian influenza virus (AIV) infections, raising the risk of zoonotic transmission to humans.
To understand the situation better, the team conducted a systematic review of literature from 2004 to 2024, focusing on the epidemiology and global spread of AIV in cats.
‘New and unknown transmission routes’
From their review, 48 articles discussed 607 AIV infections affecting 12 feline species—from house pets to tigers—with 302 leading to death across 18 countries. Half of these cases were from Asia, followed by Europe and North America. H5N1 clade 2.3.4.4b infections were documented in several countries, including Finland, France, and the U.S., involving domestic cats, bobcats, lynxes, caracals, and lions.
There was a noticeable increase in AIV infections among domestic cats in 2023 and 2024, coinciding with the appearance of H5N1 clade 2.3.4.4b.
The authors noted this increase matched the rise in transmission of the clade among birds and mammals. Most feline infections were recorded in settings like zoos and animal shelters, with about 62.6% involving domestic cats, and a staggering 71.3% of confirmed PCR cases resulted in fatalities. Many infections seemed to stem from bird-to-cat contact, primarily through consuming deceased birds or tainted raw chicken feed.
Interestingly, the Colorado Health Department recently reported indoor-only domestic cats contracting H5N1 clade 2.3.4.4b without any known contact with infected animals. This raises alarms about potential new transmission methods.
High death rate
Of the feline AIV cases, 92.3% were classified as highly pathogenic avian influenza (HPAI), with a near-total death toll among PCR-confirmed cases. Within the infections linked to HPAI H5N1, a significant portion hailed from clade 2.3.4.4b, and over half of these cases resulted in death.
Symptomatically, respiratory and neurological issues were prevalent, with some infected domestic cats suffering from blindness and inflammation of the eye due to contracting the virus from contaminated dairy products. There have also been reports of subclinical infections.
The authors suggested that the way cats are exposed and the dosage of the virus might influence both disease severity and presentation.
Infections expected to rise
Concern grows over avian flu outbreaks in dairy cattle, as infections mainly have occurred in carnivorous or omnivorous mammals. They noted that transmission to herbivores, which is often linked to food consumption, indicates alternative transmission routes, including cattle-to-cattle spread.
The infection of ruminants eliminates the likelihood of transmission from predation or scavenging, hinting at additional transmission pathways.
With avian flu having infected 950 people globally, resulting in a 50% mortality rate, the researchers highlighted that the U.S. reported 66 human cases and one death since April 2022. Dr. Kristen Coleman, the lead author, emphasized the evolving nature of the virus and the importance of monitoring as summer approaches, fearing an uptick in cases in farms and wildlife.
There’s particular alarm about the virus reaching animal shelters, which could lead to significant outbreaks affecting people, reminiscent of issues faced in New York City in 2016 with a different strain of avian flu.
Cases likely an underestimate
No human-to-human avian flu transmission has been documented yet, but the researchers are concerned that as the virus evolves, airborne transmission might become possible.
We believe this phenomenon is underreported and stress that increased surveillance of domestic cats is crucial.
Future research will focus on assessing the prevalence of HPAI and other influenza variants in at-risk cat populations, particularly those in dairy barns. Current testing typically occurs post-mortem, and many cats exhibit severe symptoms resembling rabies, which can lead to misdiagnoses.
The authors concluded that as feline-to-human transmission of AIV has been observed, various transmission routes pose heightened risks for owners, veterinarians, zookeepers, and animal shelter staff during outbreaks.
